1. Field of the Invention
This invention relates generally to safety nozzles employing fluids, more specifically to supersonic nozzles for air guns that may be used for digging in dirt and similar substances, and/or for sonic and subsonic nozzles for air guns used for cleaning and other purposes.
2. Background Information
Compressed air guns, also called air blow guns and air jet guns, are used in a variety of work environments, including sonic air guns, subsonic air guns and supersonic air guns. They are often used for cleaning purposes. Unfortunately, misuse of these devices can result in serious injuries.
Compressed air is extremely forceful, with pressures used in the workplace typically ranging from 80 to 120 pounds per square inch (psi), and even higher in certain applications. The primary concern associated with using air at this pressure is the potential to “dead-end” or block the tip of an air gun. If the gun is “dead-ended” against the skin, compressed air can enter the body through small cuts or punctures. Results can range from no damage to soft tissue damage to an embolism (air bubble in the bloodstream). Compressed air can also rupture internal organs if introduced into a body cavity, such as a nostril or ear.
In order to protect users, the static pressure at the tip of a blocked air gun must be limited to less than 30 psi. OSHA developed and issued requirements for the safe use of air guns intended for cleaning in the event of accidental or deliberate use against unprotected human skin. This requirement is that in the event of such a nozzle being placed against unprotected human skin, that the resulting pressure at the air gun exit not exceed 30 psig. Pressures below this level are not considered to represent a health hazard.
One option for meeting the safety requirement is to limit the line pressure flowing into the gun to less than 30 psi, but this pressure level is normally not practical for many applications beyond cleaning. See for example an air gun design having flow pressure reduction in stages, prior to the flow exiting the cleaning nozzle in U.S. Pat. No. 3,814,329.
Another option is the use of a projection of a mechanical structure a safe distance beyond the nozzle exit as seen in U.S. Pat. Nos. 3,888,422, 3,963,180, and 4,036,438, which are incorporated herein by reference. Again this solution limits the applicability of the resulting air gun.
U.S. Pat. No. 4,721,249 discloses an air gun design wherein a single source air supply feeds a plurality of small jets in substantial linear array. This design is also not practical for many air gun applications.
The other option is to use an air gun with a specially designed safety tip. These guns are equipped with relief ports that reduce the pressure at the nozzle to less than 30 psi if blockage occurs. Use of the safety tips is usually the preferred option since it allows cleaning work to be efficiently completed while also affording the proper level of protection. Representative examples of this solution are shown in U.S. Pat. Nos. 3,599,876, 3,647,142, 3,672,575, 3,743,186, 3,774,847, 3,790,084, 3,790,085, 4,025,045, 4,026,474, 4,243,178, and 5,285,965 which are incorporated herein by reference.
Each of the prior art air gun nozzle devices illustrating the relief port solution has the defect that during normal functional operation, the existence of a parallel open path(s) to the normal forward exiting jet stream simultaneously permits a mechanism for drawing nearby atmospheric air into the working stream that is induced by the lowering of the local pressure of the jet stream, as described by the Bernoulli equation. This joining of air flows thereby reduces the working velocity of the main stream flow, and thus diminishing it's effectiveness. When an air gun is intended to be used for cleaning purposes, this effect may not be readily apparent, but it exists. The resulting reduced air flow velocity reduces the cleaning effect for the gun which may fail to remove those objectionable materials that are more resolutely attached to the local surface to be cleaned.
This defect in the relief port safety tips of the prior art becomes increasingly significant as the working fluid stream is increased in velocity. This reaches a maximum for supersonic air nozzles used for digging in dirt and similar media. These air gun nozzles, whose velocities range usually from MACH 1 (sonic) to about MACH 2 in current applications, have this effect magnified. This is because the local pressure reduction induced by the local high velocity, increases by the square of the velocity increase as explained by the Bernoulli principle.
There remains a need in the industry to provide a fluid nozzle that contains the safety bypass features required for safe operation of air guns and the like, wherein the safety bypass features do not significantly degrade the conventional operation of the device. There is a further need in the art to increase the life of selected air gun components in harsh working environments. There is a further need to address the deficiencies of the prior art in a cost effective manner.